This
puzzle is composed of
twenty identical components that
interlock. It is much harder than it looks. As far as I know, after me George Miller was the first to
solve it. Then Toby Borland made and assembled a version of laser-cut
wood.

Here is the part design.

The above rendering might make it clearer.

Here is a stack of its components,
right out of the FDM machine,
before
separation and assembly.
If you have access to an FDM machine, you can make your own parts
from
the file available here.

There is an
article about this puzzle in issue 74 of Cubism
For Fun, which gives the secret of how I assembled it.